Vacuum type circuit interrupter

ABSTRACT

An arc extinguishing chamber confined by a cylindrical housing of stainless steel, and an insulating chamber within a hollow cylindrical insulator communicate with each other and are maintained in a vacuum with two contacts disposed in the arc extinguishing chamber. A pair of apertured separator plates respectively disposed at each end of the housing and another pair of separator plates respectively mounted on each contact rod are formed of stainless steel and prevent the insulating chamber from overheating during exhaustion at a high temperature and also from being contaminated in operation. Two heating devices are used to heat the housing to a higher temperature than the insulating chamber during the exhausting operation.

United States Patent Takeuchi et al.

Jacobs ..200/144.2

1 51 June 6, 1972 RanheimQ. ..200/144.2 Porter ..200/144.2

Primary Examiner-Robert S. Macon AttorneyRobert E. Burns and Emmanuel J. Lobato [57] ABSTRACT operation.

1 Claims, 5 Drawing Figures W I /Z I if v 1 i JJ\. a i 1 s '76 .34 I

. VACUUM TYPE CIRCUIT INTERRUPTER CROSS-REFERENCE TO RELATED APPLICATION This application relates in subject matter to the copending application Ser. No. 805,223 filed on Mar. 7, I969, by the same applicants and assigned to the same assignee.

BACKGROUND OF THE INVENTION This invention relates to a vacuum circuit interrupter of the type comprising a metallic housing defining an arc extinguishing chamber, a pair of contacts, one stationary and one movable, disposed in the housing, and an electrical insulating chamber secured to at least one end of the arc extinguishing chamber.

As all vacuum circuit interrupters are operated in a vacuum they can be expected to have the advantages including the following:

l. The overall dimension is decreased because a very small distance of separation between the contacts permits the interrupter to withstand high voltages.

2. This decrease in deminsion leads to both the simplification of the associated operating mechanism and an increase in the response speed thereof.

3. Because of the high speed at which ions produced during switching are diffused and extinguished immediately after an interruption of current flow, the interrupter is rapidly restored to its insulating state to withstand any restriking voltage, thus ensuring that it can rapidly and effectively interrupt a high currentflowing therethrough while improving the reliability of the device.

4. Both of the contacts or electrodes are maintained in a clean state at all times and are capable of always engaging each other without oxidizing thereby permitting a high current to readily flow therethrough. In addition, there is no fear that the interior of the exhausted vacuum envelope may be contaminated to deteriorate the capbility of the interrupter. Thus a long useful life is ensured without any maintenance.

Vacuum circuit interrupters having the above cited advantages are described and claimed, for example, in US. Pat. Nos.. 3,280,286. 313L705, and 3.082.307. Conventional vacuum circuit interrupters include an arc extinguishing chamber defined by a cylindrical metallic housing having a pair of contact members disposed therein, and an electrical insulator in the form ofa hollow cylinder disposed at one or both ends of the housing. It has been a common practice in the production of such devices to heat both the arc extin' guishing chamber and the insulator or insulators to the same temperature by a common heating device during the exhausting operation. On the other hand, during the operation of the vacuum circuit interrupters the components within the arc extinguishing chamber including the pair of contact members, that is to say, those portions contacting the so-called interrupting arc, are raised to the highest temperature as compared to the remaining portions of the device. Thus, it is desirable to heat those portions to a temperature substantially higher than the temperatures of the remaining portions of the interrupter or to a temperature equal to at least the said highest temperature during the exhausting operation I while the latter operation is performed for a long interval of time until the interior of the interrupter reaches the desired high vacuum. Under these circumstances. the insulator providing an electrical insulating chamber should be maintained at a temperature fairly lower than the temperature at which the above-mentioned portions are heated because of its low thermal resistance.

Furthermore, during the combined heating and exhausting operation and in the operation of vacuum circuit interrupters, a metallic vapor or vapors and scattered particles that may be formed within the arc extinguishing chamber can freely enter the associated insulating chamber to contaminate the latter. Also with the metallic housing heated to an elevated temperature, the insulating chamber can be also heated to an elevated temperature principally due to the thermal radiation from the ill housing. Practically, the metallic housing has been precluded from being heated to an elevated temperature above a temperature up to which the insulating chamber is allowed to be heated.

In order to prevent in vacuum circuit interrupters, an extraordinary voltage from occurring across a pair of contacts due to the chopping of a current upon interruption as well as to prevent the contacts from fusing to each other, it has been proposed to include a low melting-point metal such as bismuth, tellurium, antimony, silver, or the like in the material for the contacts as disclosed in US. Pat. Nos. 2,975,255 and 3,246,979. If either or both of the contacts including a low melting-point metal is or are used in vacuum circuit interrupters, the metal can be readily evaporated when the associated arc extinguishing chamber has been heated to an elevated temperature and when an electric arc has been structed across the contact members. The low melting-point metals are generally characterized by a decreased ability to withstand voltages. It is highly desirable to select the material and construction of a housing providing an arc extinguishing chamber so that the material is hardly affected with a vapor of such a low melting-point metal. It is also desirable to prevent deformation of the housing when it is subjected to a high vacuum at an elevated temperature.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention to provide a new and improved vacuum circuit interrupter including a hollow electrical insulator and a metallic housing providing an arc extinguishing chamber communicating with the interior of the insulator and capable of being heated to an elevated temperature to be exhausted to a high vacuum, thereby to increase the reliability of the interrupter.

It is another object of the invention to provide a vacuum circuit interrupter of the type as described in the preceding paragraph including improved separator means for protecting the electrical insulator against heat generated in the arc extinguishing chamber during the combined heating and exhausting operation, and for shielding the electrical insulator from an electric arc struck in the chamber in the operation of the interrupter.

It is still another object of the invention to provide a vacuum circuit interrupter including improved means for preventing the surrounding air from deforming the metallic housing when it is subjected internally to a high vacuum at an elevated temperature.

It is a further object of the invention to provide improved apparatus for and a method of heating a vacuum circuit interrupter of the type as described in the preceding paragraph such that the metallic housing is heated to an elevated temperature to be exhausted to a very high vacuum while the insu-' lation is maintained at or below the maximum permissible temperature thereof.

The invention accomplishes the above cited objects by the provision of a vacuum'circuit interrupter, comprising a pair of switching contact members, and a metallic pair of contact members disposed therein, and providing an arc extinguishing chamber characterized in that the metallic housing has disposed at least one end an electrical insulator in the form of a hollow cylinder to form an exhausted envelope, and separator means are disposed within the arc extinguishing chamber to prevent overheating of the electrical insulator during the combined heating and exhausting operation and to protect the electrical insulator against an electric arc struck in the arc extinguishing chamber.

Preferably the separator means may be formed of stainless steel and .also the metallic housing may be formed of stainless steel.

The stainless steel may advantageously be a non-magnetic stainless steel of austenitic structure consisting of at least 10 percent by weight of chromium, at least 6 percent by weight of nickel and the balance iron except for very small amounts of incidental impurities.

housing having the In a preferred embodiment of the invention, the vacuum circuit interrupter may comprise a pair of switching contact members, two rods of electrically conductive material having the contact members carried respectively at their one ends, a cylindrical housing of stainless steel providing an arc extinguishing chamber and having the pair of contact members disposed therein, an apertured metallic plate fitted into at least one end of the cylindrical housing and welded to that end, an electrical insulator in the form of a hollow cylinder closed at one end and secured at the other end to the end plate, and an apertured separator plate of stainless steel secured to the end plate on that side facing the arc extinguishing chamber and having the contact rod loosely extending therethrough to form a gap therebetween substantially equal to a minimum distance corresponding to a predetermined voltage which the interrupter must withstand.

Furthermore, another separator plate of stainless steel may be advantageously mounted on that portion of the rod disposed in the arc extinguishing chamber with a gap between the outer periphery and the adjacent portion of the cylindrical housing substantially equal to a minimum distance corresponding to a predetermined voltage which the interrupter must withstand.

In order to heat the vacuum circuit interrupters, as above described, for exhausting purposes, the invention provides a heating apparatus including first heating means for heating at least the electrical insulation, and second heating means for heating only the metallic housing to a temperature higher than a temperature to which the insulation is heated.

BRIEF DESCRIPTION OF THE DRAWING The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is an elevational view, partly in longitudinal section of a vacuum circuit interrupter constructed in accordance with the principles of the invention;

FIG. 2 is a view similar to FIG. 1 but illustrating a modification of the invention;

FIG. 3 is a fragmental elevational view, partly in longitudinal section of another modification of the invention illustrating a stationary contact member and the associated components;

FIG. 4 is a fragmental elevational view, partly in longitudinal section of still another modification of the invention illustrating a movable contact member and the associated components; and

FIG. 5 is a sectional view of a heating device for heating the vacuum circuit interrupters as illustrated in FIGS. 1 through 4 in accordance with the principles of the invention with the parts illustrated in elevation.

Throughout the FIGURES like reference numerals designate the corresponding or similar components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and in particular to FIG. 1, it is seen that the arrangement disclosed herein comprises a circularly cylindrical housing of any suitable metallic material having a pair of end plates 12 and 13 of any suitable metallic material, each said end plate including a central aperture 14 and 15, respectively, and being closely fitted into an opposing end of the cylindrical housing 10 to form an arc extinguishing chamber generally designated by the reference numeral 16. The housing 10 is preferably formed of stainless steel as described in the copending US. patent application Ser. No. 805,223 titled Vacuum Circuit Interrupter, filed on Mar. 7, 1969 by the same applicants and assigned to the same assignee as the present application. Also, the end plates 12 and 13 are preferably formed of the same material as the housing 10 and have a relatively large thickness and an outer surface substantially flush with respective end faces of the housing 10. The end plates 12 and 13 are then welded at their outer peripheral edges to the adjacent ends of the housing 10, respectively, thus ensuring a vacuum tight relationship between the housing and each of the end plates. Metallic collars 20 and 21 each have one end portion fitted in vacuum tight relationship into the central aperture 14 and 15 on the end plates 12 and 13 respectively and the other end connected in vacuum tight relationship to one end of respective electrical insulators 22 and 23 in the form of hollow cylinders. The insulators 22 and 23 may be composed of any suitable electrical insulating material such as glass or ceramic. Apertured metallic covers 24 and 25 in the form of cups are connected in vacuum tight relationship to the other ends of the insulators 22 and 23 with their mouths facing the associated insulator. The collars and covers are preferably of any suitable metallic material approximating in its coefficient of thermal expansion the material for the insulators and may be conveniently united with the respective insulators during the moulding of the latter. The metallic collars, the insulators and the metallic covers are disposed coaxially with one another and with the housing 10 to form at both ends of the latter or of the arc extinguishing chamber 16 a pair of electrical insulating chambers communicating therewith and generally designated by the reference numerals 26 and 27 respectively. Furthermore the components l0, l2, 13, 20, 21, 22, 23, 24, and 25 form a closed envelope to be exhausted.

As shown in FIG. 1, a metallic bellows 28 has one end fixed in vacuum tight relationship to one of the covers, in this example, the lower cover 25 and the other end extending into the associated insulator 23 and closed by a metallic end plate 30.

A stationary rod 32 of any suitable electrically conductive material is centrally extended and sealed through the upper cover 24 and then extended in coaxial relationship through the insulating chamber 26 until it reaches substantially the middle portion the arc extinguishing chamber 16. The stationary rod 32 has a stationary contact member 34 carried at the free end located in the chamber 16. Similarly a movable rod 33 of the same material as the stationary rod 32 centrally extends through the bellowsand lower insulating chamber 28 and 27 respectively into the arc extinguishing chamber 16 with the movable rod sealed through the end plate 30 of the bellows. Within the arc extinguishing chamber 16 the movable rod 33 is precisely aligned with the stationary rod 32 and has carried at the free end a movable contact member 35 facing the stationary contact member 34 with a gap formed therebetween. In this way the contact members 34 and 35 are approximately centrally disposed within the arc extinguishing chamber 16. Thecontacts 34 and 35 may be preferably of copper.

According to one aspect of the invention, a partition or first separator member 36 of stainless steel in the form of an annulus is fixedly secured to the inner surface of the upper end plate 12 as by welding or brazing and a second shield member 38 of stainless steel in the form of a disc is preferably fixedly mounted on the stationary rod 32 between the first member 36 and the stationary contact member 34 for the purpose as will be apparent hereinafter. Members 37 and 39 identical to the members 36 and 38 are operatively associated with the lower end plate and movable rod 13 and 33 respectively in the same manner as the members 36 and 38. The second separator members 38 and 39 each have an outside diameter larger than both the diameter of the associated central aperture 14 or 15 on the end plates 12 and 13 and the inside diameter of the associated insulator 22 and 23, while the central apertures 14 and 15 each have a diameter smaller than the inside diameter of the associated insulators 22 and 23. Both the contact rods 32 and 33 loosely extend through the respective apertures on the first shield members 36 and 37 to form gaps therebetween.

In order to exhaust the chambers 16, 26, and 27 an exhaust tube 44 is extended and sealed through one of the end plates, in the illustrated example, the upper end plate 12.

After the arrangement has been exhausted through the exhaust tube, 44 followed by the closure of the tube an operating mechanism (not shown) can be operated to move the movable contact rod 33 toward and away from the stationary contact rod 32 to put the movable contact 35 in engagement with and in disengagement from the stationary contact 34 respectively.

The are extinguishing chamber 16 provides a space serving terruption, and to prevent the contacts from fusing to each other as previously pointed out. Reference may be made to US. Pat. No. 2,975,255 and 3,246,979. The low melting-point metals are characterized in that they are less in melting and to permit the expansion of an electric arc struck between the 5 boiling points and higher in vapor pressure than copper. contact members 34 and 35 upon interrupting a current flow- Under these circumstances, the particular low melting-point ing through the interrupter, and also to rapidly diffuse and metal included in either or both of the contacts is evaporated extinguish ions caused from the electric arc and left along the to provide a high vapor pressure when the contacts are heated arc ath after the current has reduced to zero, wher b h to an elevated temperature during the combined heating and dielectric strength of the chamber is rapidly restored to 10 aus i g ope n and/o h an e ec ic arc is complete he interrupting o eration. Thu it will be a established thereacross. Such metals when evaporated are preciated that the arc extinguishing chamber is an essential generally apt to adhere to iron, nickel etc. and are also low in component governing the interrupting function of the vacuum their ability to withstand voltage. Therefore if such a low meltcircuit interrupter. ing-point metal has adhered to any portion or portions of the Also, the insulating chambers 26 and 27 and particularly the housing member 10 and associated members such as the insulators 22 and 23 function to maintain the separated conseparator members 36, 37, 38, and 39, then this leads to a tact members 34 and 35 in an electrically insulated state. decrease in the allowable voltage under which the contact Therefore, each of the insulators 22 and 23 is designed and members 34 and 35 and therefore the contact rods 32 and 33 constructed so as to have a physical dimension providing a can be maintained in an electrically insulated condition from dielectric strength sufficient to withstand any high voltage apsuch a portion or portions having the vaporized metal plied across the contact members 34 and 35 by the associated deposited thereon. electric circuit. To avoid that trouble, we have conducted many experi- It is well known that, in order to exhaust vacuum circuit inments with various metals under the same conditions in order terrupters to a high vacuum to increase the interrupting capato determine which of the metals would resist the deposition bility thereof, it is required to heat the components of the inof such low melting-point metals. The results thereof are listed terrupter to an elevated temperature sufiicient to liberate in the following Table I.

TABLE 1 Non- Weak magnetic magnetic stainless stainless Kovar Pure Pure Carbon Punsieel steel alloy nickel iron steel copper Bismuth i 2 so 70 so so 40 Tellurium l 2 50 60 60 70 gases and/0r vapors absorbed or occluded by the components during the exhausting operation. 0n the other hand, the components defining the arc extinguishing chamber 16 along with the contact members 34 and may contact the so-called interrupting arc to be raised to a maximum possible temperature higher than the temperatures of the remaining portions of the interrupter in operation. Therefore the components defining the arc extinguishing chamber along with the contact members are required to be heated to or above a maximum temperature encountered in operation while the interrupter is exhausted for a long interval of time sufiicient to obtain a desired high vacuum. This leads to the necessity of using metallic materials capable of withstanding such an elevated temperature for a long interval of time for the housing 10 and the associated members forming the arc extinguishing chamber. That is, the materials for housing member 10 and preferably for the end plates 12 and 13 should be high in thermal resistance and low in their gas permeability and susceptibility to oxidation at elevated temperatures.

It has been determined that the housing 10 formed of stainless steel can be maintained in its exhausted state at an elevated temperature for a long interval of time. It has been found also that in an atmosphere of a vacuum, even when heated to redness, stainless steels are high in mechanical strengths and, very low in oxidation susceptibility, while permitting only a very small amount of any gas t pass therethrough. Thus the housing 10 formed of stainless steel is allowed to be exhausted to a high vacuum at an elevated temperature for a long interval of time. Furthermore, it has been found that the optimum material for the housing 10 is a nonmagnetic stainless steel of austenitic structure consisting of at least 10 percent by weight of chromium, at least 6 percent by weight of nickel and the balance, iron except for very small amounts of incidental impurities.

Recently, there is the tendency to use electric contacts ineluding a low melting-point metal such as bismuth tellurium,

antimony, silver or the like in vacuum circuit interrupters in order to prevent an extraordinary voltage from occurring across the contacts due to the chopping of a current upon in- In Table l the thicknesses of bismuth or tellurium films adhering to the metals are expressed by relative magnitudes, assuming that the film adhered to the non-magnetic stainless steel as above specified is one unit thick. From Table l it is seen that bismuth and tellurium do not adhere readily to stainless steels. This is true in the case of low melting-point metals other than bismuth and tellurium. The result of experiments also indicated that the housing 10 formed of stainless steel has an inner surface characterized by high resistance to the chemical action of any vaporized metal .steel as the housing. Under these circumstances, either or both of the contact members 34 and 35 can include a low meltingtarninated with such a metal evolved with the contact members.

Since the separator members 36 through 39 are exposed to elevated temperatures and metallic vapors evolved in the arc extinguishing chamber in the combined heating operation and 1n the operation of the interrupter, they must be formed of stainless steel and preferably of a non-magnetic stainless steel of austenitic structure as previously described for the same reasons as previously described in conjunction with the material for the housing 10. The separator members 36 through 39 function to shield the associated insulation 22 or 23 or insulating chamber 26 or 27 from thermal radiation originating from the arc extinguishing chamber 16 and to prevent any metallic vapor evolved in the chamber 16 from entering the insulating chamber 26 or 27. To this end, a"

distance between each of the first separator members 36 or 37 and the associated contact rod 32 or 33 must provide the ability to withstand voltages as required for the interrupter. Also,

at least one of the distances between each of the first separator members 36 or 37 and the associated second separator member 38 or 39 and between each of the second members and the adjacent portion of the cylindrical housing must also provide the ability to withstand voltages as required for the interrupter. Moreover, such distances are required to be as small as possible. Further it is more efiective to dispose the first and second shield members within the arc extinguishing chamber 16.

It will be readily understood that the housing 10 composed of stainless steel may decrease in mechanical strengths and increase in gas permeability at elevated temperatures. In order toprevent the stainless steel housing from being deformed by the action of a compressive force externally applied thereto during the combined heating and exhausting operation, while maintaining the interior of the housing in a high vacuum as required, it is necessary to render the thickness of the housing larger than a certain limit. As a result of experiments conducted on vacuum circuit interrupters such as previously described having difierent dimensions, it has been concluded that the housing 10 must have a thickness equal to or greater than 0.5 mm for the small-sized interrupters while the greater the outside diameter of the housing the largershould be a ratio of thickness to outside diameter. If the non-magnetic stainless steelof austenitic structure as previously specified is used to form the housing it has been found that the thickness T in mm and the outside diameter D in mm must hold the following relationship- In addition, it has been determined that if the outside diameter D is equal to or greater than 240 mm, D in each of the relationships (.l (2), and (3) should be replaced by value of 240. Further it has been found that an increase in thickness of the housing 10 above a certain limit causes an increase in cooling effect and therefore improvements in the interrupting capability of the resulting vacuum circuit interrupter.

It is important that the longitudinal axes of the stationary and movable contact rods 32 and 33 respectively, are precisely aligned with each other and that the stationary and movable contactmembers 34 and 35 respectively have their opposing surfaces maintained in an exact parallel relationship, while these aligned and parallel relationships are effectively prevented from breaking down due to any deformation of the housing 10 that may occur during. the welding operation and during the combined heating and exhausting operation. To this end, the internal surfaces of both end portions of the housing 10 are preliminarily mechanically formed to have their longitudinal axes precisely aligned with each other, and the end plates 12 and 13 are closely fitted into the formed end portions of the housing. The outer peripheral edges of the end plates are preferably substantially flush with the adjacent ends 7 of the housing. Then the edges of the end plates are welded to the respective ends of the housing 10.

This measure ensures that the longitudinal axes of the internal cylindrical end surfaces of the housing 10 are precisely aligned with each other while the end portions of the housing 75 10 are free from any deformation that may occur during the succeeding welding operation for the reason that the end plates are closely fitted into the ends of the housing. Also, when the housing is heated to anelevated temperature thereby softening during the exhausting operation, each of the end plates 12 and 13 supports its associated end of the housing 10 whereby the outer peripheral surface of the end plate bears the pressure of the ambient air applied externally to the housing. Thus, the end plates 12 and 13 serve to reinforce the housing 10 preventing any deformation thereof. As a result, the interior of the housing 10 can be heated to a higher temperature for exhaustion to a high vacuum.

In operation, the longitudinal axes of the stationary and movable contact rods 32 and 33 respectively are also precisely aligned with each other while at the same time the stationary and movable contact members 34 and 35 can be in good engagement with each other under a surface pressure uniformly distributed over the entire contacting surfaces thereof with the result that both the contact members 34 and 35 are prevented from fusing to each other. The addition of a low melting-point metal to at least one of the contact members aids in preventing this fusing of the contact-members. Furthermore the bellows 28 is prevented from having a force applied along its longitudinal axis, which force would decrease its useful life. Also, at-

tendant advantages are realized in that the assembling opera-1 tion is performed in easy and rapid manner.

Referring now to FIG. 2, it is seen that first separator members 36 and 37, similar to those shown in FIG. 1 are fixedly secured to each of cup-shaped end plates 12 and 13 at the inner bottom as by welding or brazing. The end plates 12 and 13 cover each end of the cylindrical housing 10 with the mouth edges of the plates welded to the adjacent portions of the housing by welded joints 18 and 19. In other respects the arrangement is identical to that illustrated in FIG. 1 except that the second separator members are omitted.

In FIG. 3, the housing 10 is provided at one end, for example the upper end, with an inner peripheral recess 44. Then, closel'y fitted into the enlarged end of the housing 10 is an apertured end plate 12 having an annular groove 46 on the exposed surface and an annular ridge 48 disposed outside the groove 46 on the same surface and contacted on the outer peripheral side by the internal surface of the end portion of the housing 10, with the extremity of the ridge substantially flush with the end of the housing. The ridge 40 is sealed at the extremity to the end of the housing 10 by a welded joint 18.

A portion or a first separator member 36 fixed to the end plate 12 includes a hollow cylindrical portion 52 projecting into the associated insulating chamber 26 closed with a flat cover 24. A second separator member 38 in the form of a cup is mounted on stationary rod 32 with the mouth of the cup directed to a stationary contact member 34. In other respects the arrangement is identical to the corresponding portion of the arrangement as illustrated in FIG. 1.

An arrangement shown in FIG. 4 includes a housing 10 having an upper end portion 52 reduced in diameter into which an apertured end plate 12 in the form of a shallow cup is closely fitted with its bottom facing the interior of the housing. The end plate 12 is welded at the mouth edge to the reduced end of the housing 10 by a welded joint 18 bridging the end of the housing and the edge of the plate substantially flush therewith. The end plate 12, however, does not have a first shield member attached thereto. In other respects the arrangement is similar to that illustrated in FIG, 3.

Alternatively, the end portion of the housing may be enlarged in diameter.

It is to be noted that the separator member has at least one portion extending radially of the longitudinal axis of the cylin' drical housing 10, unlike the conventional type of vacuum circuit interrupters including a separator member concentric with the associated exhausted housing.

The vacuum circuit interrupter according to the invention may be assembled in the manner as will be subsequently described with reference to FIG. 1.

The stationary contact member 34, the stationary rod 32, the second shield member 38, the first shield member 36, the end plate 12'with the exhaust tube 40, the metallic collar 20, the insulator 22 and the cup-shaped cover 24 are first connected to one another to form a stationary subassembly generally designated by reference numeral 60. The longitudinal axis of the outer periphery of the end plate 12 is maintained in a precisely aligned relationship with respect'to the longitudinal axis of the rod 32, and also exactly at right angles to the contact surface of the stationary contact member 34 as previously described. The corresponding components associated with the movable contact member 35 are similarly connected to one another to form a movable subassembly generally designated by the reference numeral 61. Also the longitudinal axis of the-outer periphery of the end plate 13 is maintained in precisely aligned relationshipwith respect to the .longitudinal axis of the movable rod 33, and exactly at right angles to the contacting surface of the movable contact member 35.

Then the subassemblies 60 and 61 are united with the housing 10 by having the end plates.l2 and 13 closely fitted into the both end portions of the housing 10 with the outer peripheral edge of each plate substantially flush with the adjacent end of the housing. Those end portions have the respective internal surfaces preliminarily machined to have their longitudinal axes precisely aligned with each other and with the longitudinal axis of the housing 10. Then the end plates 12 and 13 are welded in vacuum tight relationship to the ends of the housing 10 at 18 and 19 respectively.

Thus it will be appreciated that the interrupter as assembled includes the stationary and movable rods 32 and 33 having their longitudinal axes precisely aligned with each other and with the longitudinal axis of the housing 10, while at the same time the opposing surfaces of the contact members 34 and 35 are exactly parallel to each other and precisely at right angles to the common longitudinal axes of both the rods 32 and 33.

' In other words, both the contact members are exactly centered with each other and can engage each other under a surface pressure uniformly distributed over the entire contacting surfaces thereof. Also, the end plates 12 and 13 closely fitted into the adjacent ends of the housing 10 are effective for preventing the latter from being deformed due to heat generated during the welding operation.

On the contrary, if an upside-down cup-shaped end plate is welded on the mouth to the housing 10 at an axial distance somewhat separated from the corresponding end of the housing as in the arrangement shown in FIG. 2, heat due to the welding may deform the housing. Furthermore, during the succeeding exhausting operation performed at an elevated temperature the housing may be softened and appreciably deformed because it includes no insert such as the end plate which is capable of opposing an external force such as the pressure of the surrounding air applied thereto. Such deformation may lead to an error in relative positions of the stationary and movable subassemblies 60 and 61. Therefore, in the ar rangement as shown in FIG. 2, that portion of the end portion superposing the housing is preferably as short as possible.

In order to improve the assembling accuracy with which the subassemblies 60 and 61 are assembled in the housing 10, the internal cylindrical surfaces of at least both end portions of the housing are preferably formed as by machining to have their longitudinal axes precisely aligned with each other. FIGS. 1 and 3 show the housings having been subjected to such machining operation. The arrangement of FIG. 4 includes the housing 10 having one end portion 52 reduced to a smaller diameter for the same purpose.

According to another aspect of the'invention, there is provided a heating device for heating the assembly of the interrupter, as previously described, for exhausting purposes. FIG. 5 shows by way of example such a device. The assembly is placed within a first heating device 62 including a gas burner or burners (not shown) for heating the entire body of the assembly. Then a second heating device 64 such as a gas burner or burners is disposed around the housing 10 to heat the housing and the associated member alone. If desired, the second heating device may be of the high frequency heating type. Alternatively, the movable contact member 35 may be brought into engagement with the stationary contact member 34 and a high current may be caused to flow therethrough to generate heat due to the contact resistance across the contact memrs. In any event the housing 10 and the associated members can be heated to a temperature higher than a temperature at which the components forming the insulating chambers 18 and 19 are heated by the first heating device 62. It will be appreciated that the shield members operate as previously described.

Simultaneously the exhaust tube 40 is connected to any suitable exhausting device, asfor example a vacuum pump (not shown), to exhaust the interior of the assembly until it reaches the desired degree of vacuumfl'hen the exhaust tube 40 disengages from the vacuum pump and is simultaneously closed in vacuum tight relationship, thus completing the vacuum circuit interrupter.

What we claim is:

1. In a vacuum circuit interrupter, the combination comprising a pair of switching contact members, a metallic housing having said pair of contact members disposed therein and providing an arc extinguishing chamber, a hollow cylinder of electrical insulation material disposed outside of and connected to one end of said housing to extend axially therefrom and to provide an electrical insulating chamber, sealing means connected to said cylinder and housing to permit the volume within said cylinder and housing to be exhausted, radially extending separator means mounted within said arc extinguishing chamber to inhibit heat transfer from said extinguishing chamber to said insulating chamber and to shield said insulating chamber against an electric arc struck across said pair of contact members, and an apertured end plate fitted into and welded to one end of said metallic housing, wherein said separator means comprising a first apertured separator plate attached to said end plate within said are extinguishing chamber, an electrically conductive rod carrying one of said contact members and extending through said apertured separator plate, said rod being radially spaced from said apertured separator plate to form a gap therebetween corresponding to a minimum distance sufficient to maintain the required voltage applied to said interrupter, and a second separator plate mounted on said rod within said arc extinguishing chamber and axially spaced along said rod from said first separator plate, said second separator plate having an outer periphery which is spaced from said housing within said extinguishing chamber, wherein the spaces between said separator plates and between said second separator plate and housing correspond to minimum distances sufficient to maintain the required voltage. I 

1. In a vacuum circuit interrupter, the combination comprising a pair of switching contact members, a metallic housing having said pair of contact members disposed therein and providing an arc extinguishing chamber, a hollow cylinder of electrical insulation material disposed outside of and connected to one end of said housing to extend axially therefrom and to provide an electrical insulating chamber, sealing means connected to said cylinder and housing to permit the volume within said cylinder and housing to be exhausted, radially extending separator means mounted within said arc extinguishing chamber to inhibit heat transfer from said extinguishing chamber to said insulating chamber and to shield said insulating chamber against an electric arc struck across said pair of contact members, and an apertured end plate fitted into and welded to one end of said metallic housing, wherein said separator means comprising a first apertured separator plate attached to said end plate within said arc extinguishing chamber, an electrically conductive rod carrying one of said contact members and extending through said apertured separator plate, said rod being radially spaced from said apertured separator plate to form a gap therebetween corresponding to a minimum distance sufficient to maintain the required voltage applied to said interrupter, and a second separator plate mounted on saId rod within said arc extinguishing chamber and axially spaced along said rod from said first separator plate, said second separator plate having an outer periphery which is spaced from said housing within said extinguishing chamber, wherein the spaces between said separator plates and between said second separator plate and housing correspond to minimum distances sufficient to maintain the required voltage. 